Refrigerant Mass Flow from Capacity and Refrigeration Effect
The mass flow refrigerant-velocity takes as a given, derived: m_dot = Q / (h1 - h4), the cooling load over the refrigeration effect off the P-h diagram. A 5-ton system with a 60 Btu/lb effect circulates 16.7 lb/min (1,000 lb/h) - the flow the compressor pumps and a tech hands to the velocity check. Warm the liquid line so the effect drops to 50 Btu/lb and the same 5 tons needs 20% more mass flow, the penalty of poor subcooling. Enter the enthalpies from the P-h diagram; steady flow. An engineering aid; the refrigerant property data govern.
Formula and source
Q_btumin = (unit == tons) ? Q x 200 : Q/60; RE = h1 - h4; m_dot = Q_btumin / RE; m_dot_lbh = 60 m_dot.
The refrigerant mass-flow-from-capacity relation m_dot = Q / (h1 - h4) with the refrigeration effect off the pressure-enthalpy diagram, a standard refrigeration-cycle result, by name.
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